Light pens are often used as input devices with graphic user interfaces, see Myers, “A Brief History of Human Computer Interaction Technology,” ACM Interactions, Vol. 5, no. 2, pp. 44-54, March 1998, for a brief history. Although light pens have been used since 1954, it was the work of Ivan Sutherland at Lincoln Laboratories, that popularized the use of light pens with computers, Sutherland, “Sketchpad: The First Interactive Computer Graphics,” Ph.D. Thesis, MIT, 1963.
As an input device, a light pen has some advantages over a mouse. The mouse is an indirect input device. Movement of the mouse on a horizontal surface causes movement of a cursor on a vertical display. The amount of movement, and speed of movement of the mouse and cursor can be different. In contrast, the pointing of a light pen is direct, and thus more intuitive.
In the prior art, the typical light pen is used with a display system as follows. Most CRT-based displays are raster scanned. Individual pixels on the display are illuminated at predetermined times depending on the location of the pixel in the scanning order. By detecting when a pixel is illuminated, the location of the pixel on the display surface can be determined. Therefore, the typical light pen includes a photo-sensor connected to a timing circuit. The timing of the sensed pixel, synchronized to the raster scanning, reveals its location. Typically, the light pen is held very close, if not in contact with screen.
Unfortunately, the traditional scanned CRT-based displays are being replaced by pixel-oriented displays, such as LCD screens, digital-mirror arrays, and organic LED technologies. These pixel-based displays are not scanned, and thus the traditional light pen technique based on the timing of the raster scan is not applicable for these newer display modalities.
Therefore, there is a need for a system and method that interfaces a light pen with a pixel-based display.